Example of validation absgtraction

ValidationExample.kt

interface Validator {
    fun validate(): Boolean
    val errorMessage: String
}

abstract class EditTextValidator(
    private val editText: EditText
) : Validator {
    final override fun validate(): Boolean {
        val isValid = isValid()
        editText.isErrorEnabled = !isValid
        editText.error = if (isValid) null else errorMessage
    }
    
    abstract fun isValid(): Boolean
}
    

class NonEmptyTextValidator(
    private val editText: EditText,
    fieldName: String
) : EditTextValidator(editText) {
    override fun isValid() = editText.text.isNotEmpty()

    override val errorMessage = "$fieldName cannot be empty."
}

class EmailValidator(private val editText: EditText) : EditTextValidator(editText) {
    override fun isValid() = Patterns.EMAIL_ADDRESS.matcher(editText.text).matches()

    override val errorMessage = "Email format does not valid."
}


fun main(args: Array<String>) {
    val name: EditText = TODO()
    val email: EditText = TODO()

    val validators = listOf(
        NonEmptyTextValidator(name, "Name"),
        NonEmptyTextValidator(email, "Email"),
        EmailValidator(email)
    )

    for (validator in validators) {
        val result = validator.validate()
        // here  you can define any behavior what is good for your case:
        // show all errors, or only first one
    }
}